Amplifier



April 9, 1935. K. POSTHUMUS AMPLIFIER Filed Aug. 23. 1929 mnmmm- INVENTdR KLMS rosTHuMus ATTORN EY Patented Apr. 9 1935 ADIPLIFIEB.

Klaas Posthumus, Eindhoven, Netherlands, alsignor to Radio Corporation of America, a corporation of Delaware Application August 23, 1929, Serial No. 387,828

In the Netherlands September 19, 1928 15 Claims. (01'. 250-20) The present invention relates to arrangements for amplifying electrical oscillations, and, more particularly, to methods of amplification without any appreciable distortion.

In an amplifier circuit arrangement, the total amplification present depends on the frequency supplied, because of the capacity of the discharge tubes used, and of the resonance curves of the oscillatory circuits present in the amplifier circuit arrangement. As the discharge tubes have curved characteristics, the amplification also depends on the amplitude of the oscillations to be amplifled. Due to these two causes, the curve shape of the voltage in the output circuit of an amplifier circuit arrangement relative tothe voltage on the input circuit shows deviations which, for example in testing curves and in the transmission and reception of sound vibrations, are undesirable.

The invention has for its main object an amplifying arrangement for obtaining a shape-true i. e., undistorted amplification or, if desired, an amplification obeying a definitelaw.

According to the invention, an :rth-portion of the output voltage (in which a: is small relative to the degree of amplification of the amplifying circuit arrangement), is coupled back in counteracting sense to the primary side of the amplifier circuit arrangement.

The novel features which I believe to be characteristic of my invention are set forth in particu larity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be imderstood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into efiect.

The invention will be described more fully with reference to the accompanying drawing in which the Figures 1 and 2 n v represent, by way of example, an embodiment of the invention.

Fig. 1 is a single tube l y ng circuit-ent a discharge tube I andanimpedaneei- Thevottagev tobeam plifldJsfurmmplebyasourcefiof current. Thevoltageisappliedtothe grid of the tube I and is by the snidtubelandlrytheSinsucha manner that the output vdiage V: '5 equal to mvlifaflactitnotflleoutputvoltagewerenot coupled back into the input circuit at the amplivoltages in the input circuit are in opposition so that the voltage to be amplified is in which indicates the fraction of the output voltage which is fed back. The voltage in the output circuit If, consequently, the possible amplification, m, of the total amplifier circuit arrangement is large with relation to :c, the factor will be much larger than 1, so that V: is equivalent to $.V1.

If a: has a constant value, as indicated in the drawing, in which x 1+ z the voltage V: in the output circuit of the amplifler circuit arrangement will be independent of the frequency both in phase and in amplitude, and of the amplitude of the voltage to be amplified owing to which consequently a shape-true amplification is obtained. If desired, the amplification may be dependent on the frequency in phase as well, as in amplitude, by replacing the resistances R1 or R: by an inductance or a capacity, or by both of them, while the amplification of the amplifier circuit arrangement may be made dependent on the amplitude of the voltagesto be amplifiedbyleadingbackafractionof the voltage in the output circuit, for example, throughadischargetubeoranctherdevicewhose characteristic is dependent on the amplitude.

Figzshowsantinwhichthereis obtainedalinearampliflcationofa directvolt-' age, or of slowly fluctuating voltages. As shown, suehavoltageisappliedbetweencontactsland 8, andiswiththeaidofahigh-frequency. or a -frequency carrier wave supplied, for example by an oscillator 9. This is done by applying said wave and the direct voltage, to be amplified, to the input circuit of a discharge tube IZ. A condenser It, provided in the input circuit of the tube I 2, prevents a shortcircuit of the direct voltage between the contacts 1 and 8 through an inductance H. A battery l6 serves to apply the necessary grid bias to the grid of the tube 12 so that the latter will opcrate-in the bent portion of its characteristic.

The oscillations, amplified and modulated, in the tube I2 are applied to the grid of a detector tube l5 through circuits l3 and H which are timed to the frequency of the carrier oscillation. In parallel with the output circuit of this detector is mounted a condenser l6, if desired connected in series with an inductance IT, for short-circuiting the high-frequency or-mediumfrequency component of the output energy of the detector.

Between the direct voltage on the terminals of the resistance I8 in the outputcircuit of the detector l5, and the voltage between the contacts I and 8 there is, however, no linear relation. According to the invention, this is obtained by coupling back to the primary side of the circuit arrangement a fraction of the voltage in the output circuit of the total amplifier circuit arrangement, as shown in Figure 2, by means of connectinglines l9 and 20.

Although only two modifications are shown, the invention can be applied to any known amplifier circuit arrangement both for multi-stage circuit arrangements, and for highand low-frequency amplifier circuit arrangements with transformer, resistance, and choke-coil amplification.

- If, however, the feeding-back of the energy into the input circuit cannot be effected without the production of spontaneous oscillations, it is necessary to provide in the amplifier circuit arrangement filters whereby pre-determined frequencies ages which consists in modulating a local high frequency carrier current with said direct current, amplifying the modulated carrier, detecting the amplified, modulated can'ier, and reversely feeding back a fraction of the detected current whose reciprocal is small relative to the degree of amplification of the amplifier to the input of the amplifier.

2. In a high frequency system, a tube provided with a tuned circuit in its anode circuit, a source of locally produced oscillations coupled to the input electrodes of said tube, a source of energy for modulating said oscillations coupled to said electrodes, a rectifier tube having a tuned circuit between its input electrodes, both said tuned circuits being magnetically coupled and timed to the same frequency, a resistor in the anode circuit of the rectifier, and a direct current connection between an input electrode of said first tube and a predetermined point of said resistor for impressing on said last named input electrode potential variations due to the rectified modulated oscillations.

3. A method of operating an amplifier to obtain linear amplification of a fluctuating voltage which consists in impressing local'high frequency carrier oscillations and said voltage on the amplifier whereby said carrier is modulated in accordance with the fluctuations, detecting the modulated carrier, and feeding back in a reverse sense a part of the detected output whose reciprocal is small relative to the degree. of amplification of the amplifier to the amplifierjnput.

4. A method of operating an amplifier to obtain linear amplification of a fluctuating voltage which consists in impressing local high frequency carrier oscillations and said voltage on the amplifier whereby said carrier is modulated in accordance with the fluctuations, detecting the modulated carrier, and reversely feeding back a part of the detected output voltage which is related in a predetermined manner to the degree of amplification of the amplifier to the amplifier input.

5. An amplifier for fluctuating voltages comprising an amplifier tube, means for impressing said voltages on the tube input, means for impressing a. local high frequency carrier current on the input, a detector tube coupled to the amplifier output, and means for reversely feeding back to the amplifier input a part of the detector output whose reciprocal is small relative to the degree of amplification of the amplifier.

6. An, electrical system comprising an amplifier provided with an input and output circuit, means for impressing on the input circuit an alternating current voltage, an impedance in said output circuit, and means for impressing upon the input circuit, in phase opposition to the said voltage, a fraction of the voltage developed across said impedance whose reciprocal has a predetermined small relation to the amplification power of said amplifier. I

'7. A method of operating an electron discharge tube amplifier to neutralize inherent distortion thereof consisting in impressing currents upon the amplifier, detecting the amplified currents, and impressing a predetermined fraction of the detected currents which is small with respect to the amplification factor of the amplifier, upon the amplifier to neutralize said distortion, and maintaining said fraction constant in magnitude to render the amplified currents independent of the amplitude of the first named currents.

8. A method of operating an electron discharge tube amplifier to neutralize inherent distortion thereof consisting in impressing currents upon the amplifier, detecting the amplified currents, and impressing a predetermined fraction of the detected currents which is small with respect to the amplification factor of the amplifier, upon the amplifier to neutralize said distortion, said fraction being impressed upon the amplifier in phase opposition to the first named currents.

9. A method of operating an electron discharge tube amplifier to neutralize inherent distortion thereof consisting in impressing currents upon the amplifier, detecting the amplified currents, and impressing a predetermined fraction of the detected currents upon the amplifier to neutralize said distortion and maintaining the product of the amplification power of said amplifier and the said fraction substantially greater than unity.

10. A methodof operating an electron discharge tube amplifier to neutralize inherent distortion thereof consisting in impressing currents upon the amplifier, detecting the amplified currents, and impressing a predetermined fraction of the detected currents upon the amplifier to neutralize said distortion and maintaining the magnitude of said fraction at such a value that amplified currents are equal tothe product of the reciprocal of the fraction and said first named currents.

11. A high frequency system comprising an amplifier tube, a source of high frequency energy to be amplified coupled to the grid and cathode of said tube, a resonant network, tuned to the frequency of said energy, in the anode circuit of said tube, a succeeding tube, a resonant network, tuned to said frequency, connected between the input electrodes of said second tube, said networks being coupled, means connected to the input electrodes of the second tube to operate the latter as a detector, a resistor in the anode circuit of said detector tube, and direct current connections between said resistor and the said grid and cathode of the amplifier tube for impressing on the latter a fraction of the potential variations due to the detected amplified high frequency entween the input electrodes of said second tube,-

said networks being coupled, means connected to the input electrodes of the second tube to operate the latter as a detector, a resistor in the anode circuit of said detector tube, and direct current connections between said resistor and the said grid and cathode of the amplifier tube for impressing on the latter potential variations due to the detected amplified high fre quency energy.

13. A high frequency system comprising an amplifier tube, a source of high frequency energy to be amplified coupled to thegrid and cathode of said tube, a resonant network, tuned to the frequency of said energy, in the anode circuit of said tube, a succeeding tube, a resonant network tuned to said frequency, connected between the input electrodes of said second tube, said networks being coupled, means connected tothe input electrodes of the second tube to operate the. latter as a detector, a resistor in the anode circuit of said detector tube, and adjustable direct current connections between saidresistor and the said grid and cathode of the amplifier tube for impressing on the latter a fraction of the potential variations due to the detected amplified high frequency energy which is small compared to the degree of amplification of the amplifier.

14. In a high frequency system, a tube provided with a tuned circuit in its anode circuit, a source of locally produced oscillations coupled to the input electrodes of said tube, a source of energy for modulating said oscillations coupled" to said electrodes, a detector tube having a tuned circuit between its input electrodes, both said tuned circuits being magnetically coupled and tuned to the same frequency, a resistor in the anode circuit of the detector, and a direct current connection between the grid of said first tube and a predetermined point of said resistor for impressing on said last named grid potential variations due to the detected modulated oscillations.

15. In a high frequency system, an electron discharge tube provided with atuned circuit in its anode circuit, a source of locally produced oscillations electrically coupled to said tube, a

source of energy for modulating said oscillations cillations.

KLAAS POSTHUMUS.

DISCLAIMER 1,96,830.Klaas Posthumus, Eindhoven, Netherlands. AMPLIFllER. Patent dated April 9, 1935. Disclaimer filed January 19, 1938, by theassignee, Radio Corporation of America.

Hereby enters this disclaimer to claim 6 in said specification and to the methods covered by claims 7, 8, 9, and 10 of said patent, except when each of the methods of said claims is limited to detection b5. means of an -asymmetrical conducting device for producing desired frequency changes in current.

[Qflic'ial Gazette February 8, 1.938.] 

